<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

<script>
    function fbna(n){
        if( n == 1 || n == 2){
            return 1;
        }else {
            return fbna(n-1) + fbna(n-2);
        }
    }

    console.log(fbna(25));
</script>

</body>
</html>